1. Field of the Invention
The invention concerns a device for spraying coating product such as is used for coating automobile vehicle bodies, for example.
2. Description of the Prior Art
On prior art production lines, the bodies are moved by a conveyor and the coating product sprayer machine includes a gantry supporting a horizontal beam perpendicular to the path of the bodies. This beam carries one or more coating product sprayers. These machines, often called overhead machines, are of capital importance in the coating of objects to be painted, in particular when these objects have many horizontal surfaces and surfaces perpendicular to the path of objects on the conveyor, such as the front, the hood, the roof, the trunk and the rear of an automobile vehicle body.
In some applications, for example coating with metallic paint, an overhead machine is used including a single carriage carrying one or more sprayers and moving along the beam at speed in the order of 1.5 m/s. This fast scanning movement coats all plane surfaces with a minimum number of coating product, spray air and (where applicable) high voltage supply systems.
The fast movement of the carriage on the beam creates turbulence which disturbs the flow of air near the sprayer(s). This affects the quality of the deposit and the sprayers, the carriage and the beam tend to become soiled quickly, requiring regular interruption of operation for cleaning the installation. Virtually constant surveillance of the installation and numerous manual operations are required.
In the prior art devices the carriages are driven by belts or chains on the side of the beam facing towards the bodies or on a lateral face of the beam. The fast movement of the carriage(s) detaches particles of dust or dried coating product adhering to these drive systems and because of the turbulence caused near the sprayer(s) some of these particles are deposited onto the bodies, which spoils the surface finish.
In the case of a conventional beam the carriage is sometimes asymmetrical, i.e. provided with a cantilever arm on one side only of the beam. If the beam is able to rotate about its major axis, in particular to enable the sprayer to be at all times perpendicular to the surface to be coated, including the front and the rear of the body, the asymmetry of the carriage leads to different behavior of the flow of air around the sprayer according to the direction of rotation of the beam, which is all the more difficult for the operator to control.
Finally, the prior art devices are heavy: the gantries which support the beams must be sized accordingly. They are also bulky: the flow of air in the booth is disturbed.
The invention solves all of these problems.